Fetal Development

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Welcome to your fetal development area! Here's where you can see what's happening with your baby week-by-week! Mouse over the images and see how your baby is growing! For an overview of all weeks, please click here.

First Trimester: Weeks 1-4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9 | Week 10 | Week 11 | Week 12 | Week 13 | Week 14
Second Trimester: Week 15 | Week 16 | Week 17 | Week 18 | Week 19 | Week 20 | Week 21 | Week 22 | Week 23 | Week 24 | Week 25 | Week 26 | Week 27
Third Trimester: Week 28 | Week 29 | Week 30 | Week 31 | Week 32 | Week 33 | Week 34 | Week 35 | Week 36 | Week 37 | Week 38 | Week 39 | Week 40

Weeks One Through Four

• Ovulation occurs - The time is right; now you just need this egg to be fertilized!

• Conception occurs - Did you know that during your pregnancy that your uterus will increase its capacity by 1000 times?!

• Gender is determined - Immediately upon fertilization your little one is set as a boy or a girl. Ladies, this is one that you can't take credit for since it is up to the sperm to determine the sex of your baby. Sperm carries either a "X" (girl) chromosome or a "Y" (boy) chromosome. (*Hint:* You will have to hold off on picking out the pink or blue until at least the second trimester when the gender will be visible via ultrasound.)

• Implantation - Some spotting (also known as implantation bleeding) may occur about 10 - 14 days after conception. You may believe you are starting your period but generally this bleeding is extremely light and lasts only a day or so.

• Neural tube forms - It will develop into the nervous system (Brain, spinal cord, hair, and skin). Already your baby has the foundation for thought, senses, feeling, and more!

• Heart and primitive circulatory system rapidly form - While still in its beginning stages, this is the very life support system that will carry your child throughout his or her life.

3d ultrasound images reprinted with permission from Eco-3d and SonoPortal. Embryoscopy and fetoscopy photos appearing on this web site are reproduced under "fair use" uterms for the purpose of public education.

It's simply amazing! There simply is not another word worthy to describe the development of your baby! Just think, within approximately a 40 week period, your little one will have transformed from a single cell to a fully formed human -- filled by wonderment and prepared to change your world forever. For an overview of fetal development, you can click here.

The first trimester (0 - 14 weeks), is one of the most crucial for your baby. Within this trimester you will find the most rapid rate of growth and development taking place. By the end of the 1st trimester, your son or daughter will have grown to 3.4 inches (8.7 cm) long and weigh about 1.5 ounces (43 grams). Your infant will develop everything from limbs to vital organs. Week by week the changes are astounding!

Your rate of growth in the second trimester is nothing compared to the baby's. If this rate of growth continued after birth, he or she would be thirteen feet tall at one month of age! Did you know all of baby's major organs have formed by the 15th week of pregnancy? Some, such as the heart and kidneys, will continue to develop further this trimester. Eyebrows and fingernails form. The reddish, wrinkled skin is covered with a fine hair. By the end of this trimester your baby is between 11 and 14 inches long and weighs about 2 to 2½ pounds. She can swallow and hear. You will notice periods of activity and quiet as he moves, kicks, sleeps and wakes.

By the beginning of this trimester your baby will have all of his/her bones -- 300 to be exact! Now he'll be building fat stores and muscle mass. Your baby's hair will be growing, replacing the lanugo that protected her skin in the womb. By the end of this trimester your baby will be approximately 7 pounds in weight and about 20 inches long. Her lungs mature right up to birth so don't become too anxious to deliver early. Each day in the womb, helps prepare your little one for the world outside!

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